The present invention relates to apparatus for determining the mutual positional relationship of plural patterns present in a single viewing field.
The manufacturing process for semiconductor elements such as transistors or integrated circuits (i.e. IC or LSI) includes the steps of printing of minute patterns and of lead wire bonding, in which a circuit plate or pellet has to be exactly positioned to a predetermined location. As such a circuit plate is provided with a fine structure of micron or sub-micron order, such positioning operation has also to be performed with an accuracy of micron or sub-micron order. Such operation, however, requires a two-dimensional positioning involving three parameters, i.e. two translational components x, y and a rotational component .theta., and is considerably cumbersome for the operator, requiring considerable time to acquire the expertise.
For example, in integrated circuit printing, the relative positional adjustment of a mask and a wafer is usually performed by an observation of the patterns to be aligned under a microscope and by displacing manually either said mask or wafer. The positioning or alignment is usually achieved by the observation of mutual positions of patterns in plural spots in order to enable two-demensional alignment.
However, in an alignment operation with observation of patterns in two spots, for example, at left and at right, the aligning procedure is complicated by a phenomenon that the alignment at the right spot cannot be obtained if the alignment is achieved at the left spot alone, or vice versa. In order to facilitate such aligning procedure there has recently been proposed so-called automatic aligning equipment in which the aligning operation is performed by photoelectrically detecting the determined patterns previously formed on the mask and wafer.